Method for forming an optical filter device, optical detector and optical spectrometer

Abstract

Provided is a method for forming an optical filter device. The method includes joining a stencil to a carrier. The stencil includes at least one recess. Additionally, the method includes arranging a respective optical filter in the at least one recess on the carrier. The method further includes filling a respective gap between the respective optical filter and a boundary of the respective recess with an adhesive. The adhesive is configured to prevent the passage of light. In addition, the method includes curing the adhesive and removing the carrier after curing the adhesive.

Description

[0001] Method for forming an optical filter device, optical detector and optical spectrometer

[0002] Description

[0003] Field

[0004] The present disclosure relates to optical filter devices. In particular, examples of the present disclosure relate to a method for forming an optical filter device, an optical filter device, an optical detector and an optical spectrometer.

[0005] Background

[0006] Optical detectors respond to electromagnetic radiation in a specific wavelength range depending on the material composition of the detector. To further functionalize such detectors, e.g., for spectroscopic sensing applications, filters such as optical windows or bandpass filters are employed to limit the spectral response of the detector in respect to various parameters such as the center wavelength, the Full Width at Half Maximum (FWHM) and the blocking range.

[0007] For the integration of such detectors and filters, the assemblies have to be very compact, requiring smart concepts for filter mounting and assembly, minimizing stray light and suppressing crosstalk in the case more than one detector is employed.

[0008] Hence, there may a demand for improved filter assemblies and improved manufacturing methods.

[0009] Summary

[0010] This demand is met by a method for forming an optical filter device, an optical filter device, an optical detector and an optical spectrometer in accordance with the independent claims. Advantageous embodiments are defined by the dependent claims.

[0011] According to a first aspect, the present disclosure provides a method for forming an optical filter device. The method comprises joining a stencil to a carrier. The stencil comprises at least one recess. Additionally, the method comprises arranging a respective optical filter in the at least one recess on the carrier. The method further comprises filling a respective gap between the respective optical filter and a boundary of the respective recess with an adhesive. The adhesive is configured to prevent the passage of light. In addition, the method comprises curing the adhesive and removing the carrier after curing the adhesive.

[0012] According to a second aspect, the present disclosure provides an optical filter device. The optical filter device comprises a frame. A recess is formed in the frame. Additionally, the optical filter device comprises an optical filter arranged in the frame. A gap between the optical filter and a boundary of the recess is filled with an adhesive. The adhesive is configured to prevent the passage of light.

[0013] According to a third aspect, the present disclosure provides an optical detector. The optical detector comprises a photo-sensitive sensor element sensitive to light in a predetermined wavelength range. Additionally, the optical detector comprises an optical filter device according to the second aspect. The optical filter device is configured to filter incident light before it reaches the photo-sensitive sensor element. The adhesive of the optical filter device is configured to prevent the passage of light at least in the predetermined wavelength range.

[0014] According to a fourth aspect, the present disclosure provides an optical spectrometer. The optical spectrometer comprises a light emitter configured to selectively emit light and an optical detector according to the third aspect.

[0015] According to the proposed technology, optical filter devices may be provided which allow to reduce straylight and crosstalk since voids between the optical filter and the frame / stencil are filled with adhesive preventing the passage of light. The proposed method of forming optical filter devices is simple, scalable to high production volumes, offers high flexibility without high modification effort and allows high integration at low material costs.

[0016] Brief description of the Figures

[0017] Some examples of apparatuses and / or methods will be described in the following by way of example only, and with reference to the accompanying figures, in which

[0018] Fig. 1 illustrates a flowchart of an example of a method for forming an optical filter device;

[0019] Fig. 2 illustrates the optical filter device at different stages of the method illustrated in Fig. 1 ;

[0020] Fig. 3 illustrates a first example of an optical filter device;

[0021] Fig. 4 illustrates a second example of an optical filter device;

[0022] Fig. 5 illustrates an example of an optical detector; and

[0023] Fig. 6 illustrates an example of an optical spectrometer. Detailed Description

[0024] Some examples are now described in more detail with reference to the enclosed figures. However, other possible examples are not limited to the features of these embodiments described in detail. Other examples may include modifications of the features as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe certain examples should not be restrictive of further possible examples.

[0025] Throughout the description of the figures same or similar reference numerals refer to same or similar elements and / or features, which may be identical or implemented in a modified form while providing the same or a similar function. The thickness of lines, layers and / or areas in the figures may also be exaggerated for clarification.

[0026] When two elements A and B are combined using an "or”, this is to be understood as disclosing all possible combinations, i.e. only A, only B as well as A and B, unless expressly defined otherwise in the individual case. As an alternative wording for the same combinations, "at least one of A and B" or "A and / or B" may be used. This applies equivalently to combinations of more than two elements.

[0027] If a singular form, such as "a”, "an” and "the” is used and the use of only a single element is not defined as mandatory either explicitly or implicitly, further examples may also use several elements to implement the same function. If a function is described below as implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity. It is further understood that the terms "include", "including", "comprise" and / or "comprising", when used, describe the presence of the specified features, integers, steps, operations, processes, elements, components and / or a group thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components and / or a group thereof.

[0028] Fig. 1 illustrates a flowchart of a method 100 for forming an optical filter device. The method 100 will be described in the following further with reference to Fig. 2 illustrating the optical filter device at different stages of the method 100.

[0029] The method 100 comprises joining (attaching, affixing) 102 a stencil to a carrier. The carrier is a material or substrate such as a tape or a foil for carrying the stencil and other objects. For example, the tape or foil may be based on or comprise one or more of the following: polyamide, PolyVinyl Chloride (PVC), one or more PolyOlefines (PCs) and PolyEthylene Terephthalate (PET). A thickness of the carrier may, e.g., be at least 75 pm and at maximum 200 pm. However, the present disclosure is not limited to the foregoing exemplary materials and dimensions for the carrier. The stencil is an object or material perforated with one or more recesses. In other words, the stencil comprises at least one recess. In case the stencil comprises multiple recesses, the recesses may be formed regularly (e.g., as a line or matrix array) or irregularly (i.e., with varying distances to each other) in the stencil. The recesses may exhibit the same or different dimensions or sizes (e.g., one or more of length, width and depth may vary among the recesses). For example, the respective length of the recesses may be at least 400 pm and at maximum 3000 pm. Similarly, the respective width of the recesses may be at least 400 pm and at maximum 3000 pm. The one or more recesses penetrate the stencil completely. In other words, the one or more recesses are through holes. The stencil may exhibit a (substantially) constant thickness or a varying thickness. The thickness of the stencil may, e.g., be at least 300 pm and at maximum 1000 pm. However, the present disclosure is not limited to the foregoing exemplary dimensions for the stencil and the recesses. For example, the one or more recesses formed in the stencil may be cut-outs (e.g., laser cut-out) from the material forming the stencil or the stencil including the one or more recesses may be formed by molding (e.g., injection molding) of a plastic material. Cut-outs may, e.g., be formed in case the stencil is made of metal. As indicated in the foregoing description, the stencil may be made of various materials such as metal, e.g. stainless steel, nickel, or aluminum; plastic, e.g. polyimide, polyester, polyacrylate, silicone, rubber, epoxy or polyurethane; resin, ceramics, composite materials or combinations thereof. However, the present disclosure is not limited to the foregoing exemplary materials for the stencil. The stencil may comprise a different material than the cured adhesive. The stencil may have a higher flexural modulus than the cured adhesive. The stencil may have a lower flexibility than the cured adhesive.

[0030] The stencil may be joined in various ways to the carrier. For example, joining 102 the stencil to the carrier may comprise one of gluing and laminating the stencil to the carrier. The left part of Fig. 2 illustrates the stencil 210 joined to the carrier 220. In the example of Fig. 2, the carrier 220 is a tape. The stencil 210 comprises nine recesses 211 in the example of Fig. 2. However, it is to be noted that the number of cut-outs in Fig. 2 is selected for illustrative purposes only. Any other number N > 1 of recesses may be used. The recesses 211 illustrated in Fig. 2 exhibit a square crosssection. However, it is to be noted that the present disclosure is not limited thereto. In general, the one or more recesses in the stencil may exhibit any cross-sectional shape (e.g., rectangular, oval or circular).

[0031] Additionally, the method 100 comprises arranging (placing) 104 a respective optical filter in the at least one recess on the carrier. The optical filter is a device configured (designed, adapted) to selectively transmit, absorb or reflect light at one or more specific (predetermined) wavelengths or within one or more specific (predetermined) wavelength ranges. The optical filter may be any type of filter such as a color filter, a bandpass filter, a longpass filter, a shortpass filter, a neutral density filter, a polarizing filter, an interference filter, a dichroic filter or an absorption filter. In case the stencil comprise a single recess, a single optical filter is arranged in the single recess on the carrier. In case the stencil comprise multiple recesses, a respective optical filter is arranged in each of the recesses on the carrier. The optical filters placed in the recesses of the stencil may comprise the same or different optical properties (e.g., transmit, absorb or reflect light at different wavelengths or wavelength ranges). Alternatively or additionally, the optical filters placed in the recesses of the stencil may comprise the same or different dimensions or sizes (e.g., one or more of length, width and depth may vary among the plural optical filters arranged in the plural recesses). For example, the respective length of the optical filters may be at least 400 pm and at maximum 3000 pm. Similarly, the respective width of the optical filters may be at least 400 pm and at maximum 3000 pm. However, the present disclosure is not limited to the foregoing exemplary dimensions for the optical filters. The middle part of Fig. 2 illustrates the stencil 210 joined to the carrier 220 together with nine optical filters 230 arranged in the nine recesses 211 of the stencil 210. The optical filters 230 exhibit a cube shape in Fig. 2. However, it is to be noted that the present disclosure is not limited thereto. In general, the one or more optical filters may exhibit any shape (e.g., cuboidal or cylindrical). For example, arranging 104 a respective optical filter in the at least one recess on the carrier may comprise aligning the respective optical filter with respect to the respective recess and placing the respective optical filter in the respective recess on the carrier after aligning the respective optical filter. Accordingly, the optical filters may be positioned in a controlled manner in the respective recess. The respective optical filter may be joined to the carrier (e.g., glued or laminated) to fix the position of the respective optical filter relative to the stencil for the next steps of the method 100.

[0032] As can be seen from the middle part of Fig. 2, a respective gap 240 is formed between the respective optical filter 230 and a boundary (i.e., the sidewalls) of the respective recess 211. The method 100 further comprises filling 106 the respective gap between the respective optical filter and the boundary of the respective recess with an adhesive (e.g., a glue). This is illustrated in the right part of Fig. 2. The gaps 240 between the optical filters 230 and the boundaries of the recesses 211 are filled an adhesive 250. The adhesive is a substance or material holding the stencil and the one or more optical filters arranged in the one or more recesses together by bonding them, resulting in a union that resists separation. The adhesive is configured to prevent the passage of light. In other words, the adhesive is configured to prevent light from passing through. For example, the adhesive may be configured to absorb, block and / or reflect light. The adhesive may be configured to prevent the passage of light at all wavelengths or only prevent the passage of light at one or more specific (predefined) wavelengths or wavelength ranges. For example, the adhesive may be a black adhesive (but is not restricted thereto). The adhesive may generally be applied in various forms, e.g., as a liquid adhesive, a paste adhesive or a hot melt adhesive. The adhesive may comprise various chemical compositions such as polymers, resins, or natural substances. The adhesive may, e.g., be selected based on the materials the one or more optical filters and the stencil are made up of. For example, the adhesive may be based on or comprise or consist of one or more of the following: epoxy resins, PolyUrethane (PU), Silyl Modified Polymers (SMP) or silicone.

[0033] Also, the stencil may be configured to prevent the passage of light. Like the adhesive, the stencil may be configured to absorb, block and / or reflect light. The adhesive may be made of material preventing the passage of light or be coated with material preventing the passage of light. The stencil may be configured to prevent the passage of light at all wavelengths or only prevent the passage of light at one or more specific (predefined) wavelengths or wavelength ranges. In particular, the stencil may be configured to prevent the passage of light at at least the same one or more specific (predefined) wavelengths or wavelength ranges as the adhesive.

[0034] In addition, the method 100 comprises curing 108 the adhesive and removing 110 the carrier after curing 108 the adhesive. During curing, the adhesive undergoes chemical and / or physical changes to achieve its final state (e.g., characterized by the development of strength, hardness and other desirable properties). The curing process may vary depending on the type of adhesive and its formulation. For example, chemical curing, heat curing, UV curing or combinations thereof may be used. Once the adhesive achieved its final state, the carrier is removed, i.e., separated from the stencil, the one or more optical filters and the cured adhesive affixing the one or more optical filters to the stencil. The carrier is a temporary support or substrate used to hold the stencil, the one or more optical filters and the adhesive in place, facilitate the application of the adhesive and provide structural support during curing. The carrier enables to usage of a low viscosity adhesive which can easily enter into narrow voids and thus fully wet the surface of the optical filter without leaking at the bottom. Once the adhesive has cured and reached its final state, the carrier is no longer needed and is removed. The carrier may be configured to (e.g., easily) peel away in some examples, while in other examples, additional techniques or tools may be needed / used for the removal of the carrier.

[0035] The method 100 allows to form optical filter devices which allow to reduce straylight and crosstalk since voids between the optical filter and the stencil are filled with adhesive preventing the passage of light. The method 100 is simple and comprises only a few method steps. Furthermore, the method 100 allows to speed up integration of optical detectors and optical filter devices as the optical filter device may be prepared separately (e.g., in parallel) as a subassembly and subsequently be combined with the remaining parts of the assembly. The optical filter devices may be quality controlled and only optical filter devices passing quality control may be combined with the remaining parts of the assembly (e.g., substrate, detector and coated housings with mirrors). The method 100 uses machinery, processes, equipment and consumables for the individual steps of the method that are commercially available such that the method 100 is scalable to high production volumes at low material costs (e.g., for adhesive, molded stencils or carriers like tape or foil). Additionally, the method 100 allows high integration and offers high flexibility without high modification effort.

[0036] Additionally, the method 100 is tolerant towards imperfections of the optical filters. For example, chipped edges of the optical filter may cause problems due to stray light or incorrect filtering. A curable adhesive can flow into any imperfections and reduce stray light or incorrect filtering, in particular when using an adhesive of low light permittivity such as a black adhesive. There is therefore no need to cover the imperfect edge portions of the optical filter, so the maximum surface of the optical filter can be used.

[0037] The stencil with the one or more adhered optical filters may be the final optical filter device obtained from the method 100. The stencil serves as a frame for the one or more optical filters in the one or more recesses of the stencil. In particular, if the stencil comprises a single recesses, singulation of the stencil is not required. Similarly, if an optical filter device comprising a plurality of (e.g., an array of) optical filters is desired, a stencil with a plurality of recesses may be used and the optical filters may be arranged in the recesses as described above. Also in this case, singulation of the stencil is not required. For example, after removing the carrier 220, the stencil 210 with the adhered optical filters 240 as illustrated in the right part of Fig. 2 may form the optical filter device. In alternative examples, the stencil may comprise a plurality of recesses and a plurality of optical filters may be arranged in the recesses as described above. In these examples, the stencil is singulated after curing 108 the adhesive to obtain at least one optical filter device. In other words, the method 100 may optionally comprise singulating 114 the stencil after curing the adhesive to obtain at least one optical filter device. For example, the stencil may be singulated to obtain a plurality of optical filter devices, wherein the singulated part of the stencil serves as frame for the respective optical filter device. The stencil may be singulated such that the respective optical filter device comprises one or more of the optical filters previously adhered to the stencil. Accordingly, a plurality of optical filter devices may be manufactured (formed) with the method 100 in parallel. The stencil may be singulated before, while or after removing 110 the carrier. For example, after removing the carrier 220, the stencil 210 with the adhered optical filters 240 may be singulated to obtain nine optical filter devices each comprising part of the stencil 210 as a frame and one of the optical filters 230. In other examples, the stencil 210 with the adhered optical filters 240 may be singulated to obtain three optical filter devices each comprising part of the stencil 210 as a frame and three of the optical filters 230 (e.g., each of the optical filter devices may comprises the optical filters of one line or one column in the array illustrated in Fig. 2).

[0038] In some cases, residuals of the carrier may remain on the respective optical filter and / or the stencil and / or the adhesive after removing 110 the carrier. Therefore, the method 100 may optionally further comprise performing 112 a cleaning process after removing 110 the carrier to remove possible residuals of the carrier from at least one of the respective optical filter, the adhesive and the stencil. Various cleaning processes may be used depending on the type (material) of the carrier, the joining of the stencil (and optionally the one or more optical filters) to the carrier, the type (material) of the stencil, the type (material) of the optical filter and / or the type (material) of the adhesive. For example, isopropyl alcohol (also known as isopropanol) may be used in the cleaning process to remove the possible residuals of the carrier from the respective optical filter and / or the stencil and / or the adhesive.

[0039] In the flowchart illustrated in Fig. 1, singulating 114 the stencil is shown as a step subsequent to performing 112 the cleaning process. However, it is to be noted that singulating 114 the stencil need not take place after performing 112 the cleaning process. According to examples, singulating 114 the stencil may be done before performing 112 the cleaning process.

[0040] The cross-section of the respective recess is selected so that it is slightly larger than the cross-section of the optical filter arranged in the respective recess and a gap is formed, which is filled with the adhesive. The dimensions of the respective gap may be such that capillary forces promote distribution of the adhesive in the respective gap. For example, the respective gap between the respective optical filter and the boundary of the respective recess may be 1000 m or less, 500 pm or less, 200 pm or less, or 50 pm or less. In particular, if the respective gap between the respective optical filter and the boundary of the respective recess is 200 pm or less, or 50 pm or less, capillary forces promote distribution of the adhesive in the respective gap. For example, the respective gap between the respective optical filter and the boundary of the respective recess may be 50 pm or more and 100 pm or less. Adjusting the dimensions of the respective gap so that capillary forces promote distribution of the adhesive in the respective gap is helpful in distributing the adhesive. Additionally, the adhesive forms a meniscus at the edges of the respective optical filter and fully covers them which prevents straylight. In other words, the respective gap is filled with the adhesive to fully cover side surfaces of the respective optical filter with the adhesive. Furthermore, if an optical filter has chipped edges on the bottom or top side (which may, e.g., be due to a dicing process in the manufacture of the optical filter), these voids will be filled with adhesive. This is again advantageous for straylight reduction. However, the bottom and top sides of the respective optical filter are not covered by the adhesive. This may allow to increase the resulting aperture of the optical filter device compared to conventional manufacturing methods. As indicated by the thicknesses of the stencil 210 and the optical filters 230 in the middle part and the right part of Fig. 2, a thickness of the stencil may be less than a thickness of the respective optical filter. However, the present technology is not limited thereto. In alternative examples, the thickness of the respective optical filter may be less than the thickness of the stencil. The difference in thickness may, e.g., be 100 m or less, or 200 pm or less

[0041] The foregoing description focused on the forming of an optical filter device according to the proposed technology. The following description will focus on the optical filter device itself and a few applications for the optical filter device.

[0042] Fig. 3 illustrates an exemplary optical filter device 300. The optical filter device 300 comprises a frame 310. A recess (through hole) 330 is formed in the frame 310. An optical filter 320 arranged in the recess 330. A gap between the optical filter 320 and the boundary (i.e., the sidewalls) of the recess 330 is filled with an adhesive 340.

[0043] The frame 310 may, e.g., be the above described stencil or a part thereof (e.g., after singulating the stencil). In particular, the frame 310 may be made of the same material like the above described stencil, be substantially flat and exhibit a (substantially) constant thickness. The optical filter 320 is like the above described optical filter.

[0044] The gap between the optical filter and the boundary of the recess may be as described above for the gap between the respective optical filter and the boundary of the stencil. In particular, the gap between the optical filter and the boundary of the recess may be 1000 m or less, 500 pm or less, 200 pm or less, or 50 pm or less. For example, the gap may be 50 pm or more and 100 pm or less.

[0045] The adhesive 340 may be as described above. In particular, the adhesive 340 is configured to prevent the passage of light analogously to what is described above. That is, the adhesive may be configured to prevent the passage of light at all wavelengths or only prevent the passage of light at one or more specific (predefined) wavelengths or wavelength ranges. For example, the adhesive may be a black adhesive (but is not restricted thereto).

[0046] The optical filter device 300 allows to reduce straylight and crosstalk since voids between the optical filter 320 and the frame 310 are filled with the adhesive 340 preventing the passage of light.

[0047] Like the adhesive 340, the frame 310 may be configured to prevent the passage of light. In particular, the frame may be configured to prevent the passage of light at at least the same one or more specific (predefined) wavelengths or wavelength ranges as the adhesive 340.

[0048] As illustrated in Fig. 3, the adhesive 340 forms a meniscus at the edges of the optical filter 320 and fully covers the side surfaces of the optical filter. In case the optical filter 320 has chipped edges on the bottom or top side (which may, e.g., be due to a dicing process in the manufacture of the optical filter), these voids will be filled with adhesive 340. The bottom and top sides of the optical filter 320 are not covered by the adhesive 340. The arrangement of the adhesive allows to prevent straylight and increase the resulting aperture of the optical filter device 300 compared to conventional devices.

[0049] The thickness of the frame 310 is less than the thickness of the optical filter 320 in the example of Fig. 3. However, the present technology is not limited thereto. In alternative examples, the thickness of the optical filter 320 may be less than the thickness of the frame 310. The difference in thickness may, e.g., be 100 m or less, or 200 pm or less.

[0050] The optical filter device 300 described above comprises a single optical filter 320. However, the present disclosure is not limited thereto. Optical filter devices according to the present disclosure may comprise multiple optical filters (i.e., N > 2 optical filters) adhered to a frame. An exemplary optical filter device 400 comprising nine optical filters is illustrated in Fig. 4. Like the optical filter device 300, the optical filter device 400 comprise a frame 410. In contrast to the single recess 330 formed in the optical filter device 300, nine recesses 430 are formed in the frame 410. The recesses 430 are formed or arranged regularly (as a matrix array) in the frame 410. However, the present disclosure is not limited thereto. In other examples, the recesses 430 may be arranged irregularly. The recesses 430 exhibit the same dimensions or sizes (i.e., the same length, width and depth). However, in alternative examples, the recesses may exhibit different (varying) dimensions. A respective optical filter 420 is arranged in each of the recesses 430. Like in the optical filter device 300, the respective gap between the respective optical filter 420 and the boundary of the respective recess 430 is filled with an adhesive 440 that is configured to prevent the passage of light.

[0051] The optical filters 420 arranged in the recesses 430 of the frame 410 may comprise the same or different optical properties (e.g., transmit, absorb or reflect light at different wavelengths or wavelength ranges). Alternatively or additionally, the optical filters 420 arranged in the recesses 430 of the frame 410 may comprise (exhibit) the same or different dimensions or sizes (e.g., one or more of length, width and depth may vary among the optical filters 420).

[0052] Optical filters according to the proposed technology may be used for various applications. For example, optical filters according to the proposed technology may be used for optical detectors. Fig. 5 illustrates a sectional view of an exemplary optical detector 500.

[0053] The optical detector 500 comprises a photo-sensitive sensor element (photo-sensitive pixel) 510. Optionally, the optical detector 500 may comprise one or more further photo-sensitive sensor elements such as the photo-sensitive sensor elements 550 and 560 indicated in Fig. 5. Each photo-sensitive sensor element comprises semiconductor material such as one or more inorganic photoconductive materials like lead sulfide (PbS), lead selenide (PbSe), germanium (Ge), indium gallium arsenide (InGaAs), indium antimonide (InSb) or mercury cadmium telluride (HgCdTe or MCT). Incident light 501 penetrates the semiconductor material of the respective photo-sensitive sensor element and causes generation of charge carriers (e.g., electrons or holes) and, hence, an electrical signal in the semiconductor material. For example, the one or more photo-sensitive sensor element may be Charge-Coupled Devices (CCDs) or Complementary Metal-Oxide-Semiconductor (CMOS) devices. Depending on the semiconductor material, the respective photo-sensitive sensor element is sensitive to one or more specific (predetermined) wavelengths or wavelength ranges. In case the optical detector 500 comprises a plurality of photo-sensitive sensor elements, the photosensitive sensor elements may be sensitive to the same or different wavelengths or wavelength ranges. The photosensitive sensor element 510 is sensitive to light in a predetermined wavelength range. For example, the photo-sensitive sensor element 510 may comprise PbS as photoconductive material and be sensitive to light in the wavelength range between 1 m and 3 pm. Accordingly, the photo-sensitive sensor elements 550 and 560 may be sensitive to the same predetermined wavelength range or at least one of the photo-sensitive sensor elements 550 and 560 may be sensitive to light in a different wavelength range. For example, one or both of the photo-sensitive sensor elements 550 and 560 may be sensitive to light in a second predetermined wavelength range, which is different from the wavelength range in which the photo-sensitive sensor element 510 is sensitive to light.

[0054] The optical detector 500 further comprises an optical filter device 520 according to the proposed technology. For example, the optical filter device 520 may be one of the optical filter devices 300 and 400 described above with reference to Fig. 3 and Fig. 4. The optical filter device is configured to filter the incident light 501 before it reaches the photo-sensitive sensor element 510 and optionally the one or more further photo-sensitive sensor elements of the optical detector 500 such as the photo-sensitive sensor element 550. The adhesive of the optical filter device 520 is configured to prevent the passage of light at least in the predetermined wavelength range in which the photo-sensitive sensor element 510 is sensitive to light. Optionally, the adhesive of the optical filter device 520 may further configured to prevent the passage of light in the one or more wavelength ranges in which further photo-sensitive sensor elements of the optical detector 500 such as the photo-sensitive sensor element 550 are sensitive to light. As described above, the frame of the optical filter device 520 may prevent the passage of light at least in the same wavelength range(s) as the adhesive of the optical filter device 520.

[0055] For example, if the optical filter device 520 is arranged only on top of the photo-sensitive element 510 and configured to filter the incident light 501 before it reaches the photo-sensitive sensor element 510, the optical filter device 520 may be the optical filter device 300 described above. In other words, the optical filter device 520 may comprise only a single optical filter. In case the optical filter device 520 is arranged on top of multiple photo-sensitive sensor elements, the optical filter device may comprise the same number of optical filters - one for each of the multiple photosensitive sensor elements. In other words, if the optical filter device 520 is arranged on top of U > 1 photo-sensitive sensor elements and configured to filter the incident light 501 before it reaches a respective one of the photo-sensitive sensor elements, the optical filter device 520 may comprise U optical filters adhered to the frame such that each of the optical filters filters the incident light 501 for one of the photo-sensitive sensor elements. For example, the optical filter device 400 described above may be used if the optical filter device 520 is to be arranged on top of nine photo-sensitive sensor elements.

[0056] The optical detector 500 may optionally further comprise a substrate 530 such as, e.g., a Printed Circuit Board (PCB). The photo-sensitive sensor element 510 is arranged on the substrate 530 in these examples. In case the optical detector 500 comprises a plurality of photo-sensitive sensor elements, also the other photo-sensitive sensor elements may be arranged on the substrate 530 as illustrated in Fig. 5 for the photo-sensitive sensor elements 550 and 560. However, the present technology is not limited thereto. In some examples, the optical detector 500 may comprise one or more further substrates on which one or more of the other photo-sensitive sensor elements are arranged. For example, the photo-sensitive sensor element 560 may alternatively be arranged on a separate substrate of the optical detector rather than on the same substrate 530 as the photo-sensitive sensor element 510.

[0057] A housing 540 may be arranged on the substrate 530 and surround the photo-sensitive element 510 and optionally the one or more further photo-sensitive sensor elements of the optical detector 500 such as the photo-sensitive sensor element 550. As indicated in Fig. 5, the optical filter device 520 may be mounted to the housing 540 in these examples. The housing 540 is configured to prevent the passage of light at least in the wavelength range(s) in which the one or more photo-sensitive sensor elements surrounded by the housing 540 is / are sensitive to light. The housing 540 may comprise one or more optical elements such as mirrors to focus light incident on the housing 540 after passing the optical filter device 520 on one of the one or more photo-sensitive sensor elements surrounded by the housing 540.

[0058] The optical filter device 520 and the housing 540 both allow to minimize stray light and suppress crosstalk. The term crosstalk refers to electromagnetic radiation (light) that is intended to interact with a certain photo-sensitive sensor element but instead interacts with an adjacent photo-sensitive sensor element. Electromagnetic radiation (light) that interacts with a photo-sensitive sensor element without passing the optical filter device 520 (e.g., stray light or diffracted light) further increases the crosstalk. This unwanted electromagnetic radiation (light) is suppressed by both the optical filter device 520 and the housing 540. Accordingly, distorted measurements in applications using the optical detector 500 (e.g., spectroscopic sensing applications) may be avoided.

[0059] As indicated for the photo-sensitive sensor element 560, the optical detector 500 may optionally comprise one or more further optical filter device according to the present technology for one or more of the optional further photosensitive sensor elements. The optional optical filter device 570 according to the proposed technology is configured to filter the incident light 501 before it reaches the photo-sensitive sensor element 560. Like the optical filter device 520, the optical filter device 570 may be one of the optical filter devices 300 and 400 described above with reference to Fig. 3 and Fig. 4. For example, if the second photo-sensitive sensor element 560 is sensitive to light in the second predetermined wavelength range, the optical filter device 570 may be configured to prevent the passage of light at least in the second predetermined wavelength range.

[0060] Another housing 580 may be arranged on the substrate 530 (or a separate substrate in case the photo-sensitive sensor element 560 is arranged on the separate substrate of the optical detector 500) and surround the photo-sensitive element 560 (and optionally one or more further photo-sensitive sensor elements of the optical detector 500). Optical detectors according to the proposed technology may be used for various applications. For example, optical detectors according to the proposed technology may be used for optical spectrometers. Fig. 6 illustrates a sectional view of an exemplary optical spectrometer 600.

[0061] The optical spectrometer 600 comprises a light emitter or light source 610 (e.g., a laser diode and / or a Light-Emitting Diode, LED) configured to selectively emit light 611, an optical detector 620 according to the proposed technology (e.g., the optical detector 500 described above) and a sample interface 630.

[0062] As illustrated in Fig. 6, a sample 699 may be placed on the sample interface 630. The light 611 emitted by the light emitter 610 traverses the sample interface 630 and is reflected by the sample 699. The reflected light 61 T traverses the sample interface 630 and reaches the optical detector 620. The optical detector 620 comprises one or more photo-sensitive sensor elements configured to measure the reflected light 61 T incident on the respective photo-sensitive sensor element. Based on the electrical signal (s) generated by the one or more photo-sensitive sensor elements, measurement data are generated and output by the optical spectrometer 600.

[0063] For example, for a reference measurement, a reference sample may be placed on the sample interface 630. The reference sample is a sample (object) with known spectral characteristics. The reference sample may, e.g., exhibit a 99% reflectance and diffusive (Lambertian) reflective scattering properties. The reference measurement allows to calibrate or validate the optical spectrometer 600, ensuring its accuracy and reliability. For a sample measurement, a target sample may be placed on the sample interface 630. The target sample is a sample (object) with unknown spectral characteristics. In other words, the target sample is being examined for its spectral characteristics. The target sample may be a liquid, a gas or a solid. For example, the target sample may be (e.g., human) skin, textile, a plastic or a food item. For a background measurement (also known as open port measurement), no sample is placed on the sample interface 630. The background measurement allows to determine the baseline or background that is present when no sample is present in the measurement path (i.e., the optical path) of the optical spectrometer 600. The background measurement allows to correct and account for ambient or instrumental signals that could affect the accuracy of the sample measurements.

[0064] Further elements of the spectrometer 600 such as one or more further optical filters, a beam splitter, dispersive elements like a diffraction grating or prism, or signal processing circuitry such as amplifiers or Analog-to-Digi tai Converters (ADCs) are omitted in Fig. 6 for reasons of simplicity.

[0065] The aspects and features described in relation to a particular one of the previous examples may also be combined with one or more of the further examples to replace an identical or similar feature of that further example or to additionally introduce the features into the further example.

[0066] It is further understood that the disclosure of several steps, processes, operations or functions disclosed in the description or claims shall not be construed to imply that these operations are necessarily dependent on the order described, unless explicitly stated in the individual case or necessary for technical reasons. Therefore, the previous description does not limit the execution of several steps or functions to a certain order. Furthermore, in further examples, a single step, function, process or operation may include and / or be broken up into several sub-steps, -functions, -processes or -operations.

[0067] If some aspects have been described in relation to a device or system, these aspects should also be understood as a description of the corresponding method. For example, a block, device or functional aspect of the device or system may correspond to a feature, such as a method step, of the corresponding method. Accordingly, aspects described in relation to a method shall also be understood as a description of a corresponding block, a corresponding element, a property or a functional feature of a corresponding device or a corresponding system.

[0068] The following claims are hereby incorporated in the detailed description, wherein each claim may stand on its own as a separate example. It should also be noted that although in the claims a dependent claim refers to a particular combination with one or more other claims, other examples may also include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are hereby explicitly proposed, unless it is stated in the individual case that a particular combination is not intended. Furthermore, features of a claim should also be included for any other independent claim, even if that claim is not directly defined as dependent on that other independent claim.

Claims

ClaimsWhat is claimed is:

1. A method (100) for forming an optical filter device, the method (100) comprising: joining (102) a stencil to a carrier, the stencil comprising at least one recess; arranging (104) a respective optical filter in the at least one recess on the carrier; filling (106) a respective gap between the respective optical filter and a boundary of the respective recess with an adhesive, the adhesive being configured to prevent the passage of light; curing (108) the adhesive; and removing (110) the carrier after curing (108) the adhesive.

2. The method (100) of claim 1, wherein joining (100) the stencil to the carrier comprises one of gluing and laminating the stencil to the carrier.

3. The method (100) of claim 1 or claim 2, wherein arranging (104) the respective optical filter in the at least one recess on the carrier comprises: aligning the respective optical filter with respect to the respective recess; and placing the respective optical filter in the respective recess on the carrier after aligning the respective optical filter.

4. The method (100) of any one of claims 1 to 3, wherein the respective gap between the respective optical filter and the boundary of the respective recess is 1000 pm or less, 500 pm or less, 200 pm or less, or 50 pm or less.

5. The method (100) of any one of claims 1 to 4, further comprising: performing (112) a cleaning process after removing the carrier to remove possible residuals of the carrier from at least one of the respective optical filter and the stencil.

6. The method (100) of any one of claims 1 to 5, wherein the stencil comprises a plurality of recesses, and wherein the method (100) comprises singulating (114) the stencil after curing the adhesive to obtain at least one optical filter device.

7. The method (100) of any one of claims 1 to 6, wherein the respective gap is filled with the adhesive to fully cover side surfaces of the respective optical filter with the adhesive.

8. An optical filter device (300, 400), comprising: a frame (310, 410), wherein a recess (330, 430) is formed in the frame; and an optical filter (320, 420) arranged in the recess (330, 430), wherein a gap between the optical filter (320, 420) and a boundary of the recess (330, 430) is filled with an adhesive, and wherein the adhesive (340, 440) is configured to prevent the passage of light.

9. The optical filter device of claim 8, wherein the frame (310, 410) is configured to prevent the passage of light in at least the same wavelength range as the adhesive (340, 440).

10. The optical filter device of claim 8 or 9, wherein side surfaces of the optical filter (320, 420) are fully covered with the adhesive (340, 440).11 . The optical filter device of any one of claims 8 to 10, wherein the gap between the optical filter (320, 420) and the boundary of the recess (330, 430) is 1000 m or less, 500 pm or less, 200 pm or less, or 50 pm or less.

12. An optical detector (500), comprising: a photo-sensitive sensor element (510) sensitive to light in a predetermined wavelength range; and an optical filter device (520) according to any one of claims 8 to 11, wherein the optical filter device (520) is configured to filter incident light (501) before it reaches the photo-sensitive sensor element (510), and wherein the adhesive of the optical filter device (520) is configured to prevent the passage of light at least in the predetermined wavelength range.

13. The optical detector (500) of claim 12, further comprising a substrate, wherein the photo-sensitive sensor element (510) is arranged on the substrate (530), wherein a housing (540) is arranged on the substrate (530) and surrounds the photo-sensitive element (510), and wherein the optical filter device (520) is mounted to the housing (540).

14. The optical detector (500) of claim 12 or claim 13, further comprising: a second photo-sensitive sensor element (560) sensitive to light in a second predetermined wavelength range; and a second optical filter device (570) according to any one of claims 8 to 11, wherein the second optical filter device (570) is configured to filter the incident light (501) before it reaches the second photo-sensitive sensor element (560), and wherein the adhesive of the second optical filter device (570) is configured to prevent the passage of light at least in the second predetermined wavelength range.

15. An optical spectrometer (600), comprising: a light emitter (610) configured to selectively emit light (611); and an optical detector (620) according to any one of claims 12 to 14.

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